There are multiple risks which can be unnoticeable and therefore ignored until it is too late. Identity theft or fraudulent use of your credit card/banking details could occur if your Anti Virus has reached the end of its trial period, or the full working program subscription has come to the end of its contract.

Alternatively your computer will become slow or randomly shut down and restart.  You may have to wait ages for your computer to start up or shut down. Any or all are signs of a possible virus.